The invention concerns an actively shielded gradient coil system for use in a magnetic resonance device, comprising a main field magnet which generates a main magnetic field that is oriented in the direction of a z-axis, wherein, when a current flows, the gradient coil system generates a gradient field in a measuring volume through which the z-axis extends, wherein the gradient coil system comprises a main coil, a shielding coil and at least one correction coil, wherein the active conductor elements of the main coil and of the shielding coil, which contribute to the gradient field when a current flows, each take up spatial areas in a plane perpendicular to the z-axis, wherein the partial area taken up by the main coil extends in a radial direction with respect to the z-axis from r_min_1(z) to r_max_1(z) (with r_min_1(z) r_max_1(z)), wherein the partial area taken up by the shielding coil extends in a radial direction with respect to the z-axis from r_min_2(z) to r_max_2(z) (with r_max_1(z) r_min_2(z) r_max_2(z)), wherein the mentioned radial partial areas are occupied by active conductor elements in more than half of the azimuthal angle range with respect to the z-axis, and wherein the active conductor elements of the correction coil are arranged in planes perpendicular to the z-axis in each case outside of the radial partial area of the main coil and outside of the radial partial areas of the shielding coil.
A gradient coil system of this type is disclosed e.g. in U.S. Pat. No. 5,742,164 (document [7]).
FIG. 3 shows in principle the prior art described in [7].
Further radial partial areas r_min_n(z) to r_max_n(z) may also be taken up by the shielding coil, wherein r_max_(n−1) (z)≦r_min_n(z)≦r_max_n(z) and n>2 is a natural number, which, however, is not disclosed in [7]. Shielding coils which take up further radial partial areas are familiar to the expert as is illustrated e.g. in FIG. 1 in [11].